The UK National Institute of Health and Care Excellence (NICE) recommends the use of CKD–EPI for the majority of patients [67], but for the assessment of eGFR in those with CKD stage 3a (eGFR 45–59 mL/min/1.73 m2) and no proteinuria, the use of cystatin C-based equations is recommended [68]. Here, CST3 is linked to chronic kidney disease.